1. Field of the Invention
The present invention relates to a toner for use in an image forming method intended for visualizing an electrophotograph, or an electrostatic charge image.
2. Description of the Related Art
A large number of image forming methods such as an electrostatic recording method, a magnetic recording method, and a toner jet method have been conventionally known. The electrostatic recording method generally involves: utilizing a photoconductive substance to form an electrostatic latent image on a photosensitive member by various means; next, developing the latent image with toner to provide a visible image; transferring the toner onto a transfer material such as paper as required; and then fixing the toner image onto the transfer material by using heat, pressure, or the like to provide a copied article. The toner remaining on the photosensitive member without being transferred is cleaned by various methods, and then the above-mentioned steps are repeated.
Various methods and devices have been developed for the step of fixing the toner image onto a sheet such as paper, as the above-mentioned final step. The method most commonly used in recent years is a pressure heating mode using a fixing roller. The pressure heating mode using a fixing roller involves passing the transfer material while bringing surfaces of a pressure roller and the heat roller having releasability with respect to toner and a surface of a toner image on the transfer material into contact with each other under pressure to fix the toner image. In the mode, the surface of the fixing roller and the toner image on the transfer material are brought into contact with each other under pressure, so the mode provides extremely good thermal efficiency upon fusion of the toner image onto the transfer material, and allows fixation to be quickly performed. However, in the above method, the surface of the fixing roller is brought into contact with the toner image in a molten state under pressure. Thus, part of the toner image may be adhered on and transferred to the surface of the fixing roller and then retransferred to a subsequent sheet to be fixed. As a result, it may cause a so-called offsetting phenomenon and contaminate the fixing sheet. Therefore, the heat roller fixing system has been required to prevent the toner from adhering on the surface of the fixing roller.
Accordingly, for the purpose of preventing toner from adhering on the surface of a fixing roller, for example, the roller surface has been formed with a material (such as a silicon rubber or a fluorine-based resin) which is excellent in releasability with respect to the toner. Further, the surface of the roller has been covered with a thin film made of a liquid having high releasability, such as silicone oil or fluorine oil, to prevent an offset from occurring and to prevent the surface of the roller from fatigue. However, this method is very effective in preventing the offset of toner but requires a device for supplying an offset-preventing liquid. Thus, the method has a problem of a complicated fixing device and also a problem of causing a detachment between the layers constituting a fixing roller due to the application of oil. As a result, the method has been always accompanied by an adverse effect of facilitating the shortening of the life of the fixing roller.
Further, it has a high potential for an evaporation of silicone oil or the like with heat to cause problems of contaminating the inside the device, treating collected oil, and so on. Thus, instead of using a device for supplying silicone oil, or the like, in consideration of supplying from toner a liquid for preventing an offset from occurring upon heating, some documents (for example, JP 55-153944 A and JP 09-73187 A) disclose a method of adding a substance having a releasability, such as low-molecular weight polyethylene and low-molecular weight polypropylene, to the toner. However, the addition of such an additive in large amount to exert a sufficient effect may cause actual problems: a filming phenomenon to a photosensitive member; and surface contamination of toner carrying members, such as a carrier and a sleeve, because of resulting in image deterioration. Thus, a small amount of wax not enough to cause image deterioration is added to toner in combination of the use of a device that utilizes a member (such as web-like member) for supplying a small amount of releasable oil or rolling up an offset toner or a device that utilizes a cleaning pad for cleaning. However, considering the latest demands of miniaturization, weight-saving, and high-reliability, it is desirable and preferable to remove these auxiliary devices. Therefore, further improvements in properties of toner fixation, offset, and soon should be required as countermeasures. However, such improvements are hardly realized as far as further improvements in binder resin, wax, and the like of toner are not achieved.
Further, in recent years, opportunities have increased to output image data incorporated by digital cameras, digital video cameras, portable terminals, and the like or output graphic images such as posters from image-forming apparatuses, such as copying machines and digital LBPs. Therefore, there is an increased need of generating the output of an image all over the sheet of paper in a manner similar to the quick-printing or development of the conventional optical film camera. For coping with the needs from market, the addition of an image-forming mechanism corresponding to a whole-surface frameless image has been proposed (see, for example, JP2003-98915A and JP2004-45457A). In the case of an image formation corresponding to a whole-surface frameless image, in particular when a recording material having no margin on the edge thereof is rushed into a fixing nip part, there is a tendency of generating a so-called “twisted offsetting phenomenon” in which a toner image on the recording material is not separated from a heat member.
Further, in the case of responding to a request for speeding-up in recent years, in addition to speeding up the transfer of a recording material, the distance (paper gap) between the sheets of the recording material to be fed one by one tends to become shorter. In addition, the temperature of the recording material discharged after the fixation becomes very high. In general, after the fixation, the recording material is discharged from a discharge roller and then mounted on a discharge tray or a stacker capable of carrying the sheets of the recording material in large numbers. Therefore, when the large numbers of the sheet of the recording material being heated at high temperature are mounted on the stacker in a short time, the once-fixed toner is melted by re-accumulated heat, thereby, a phenomenon in which the sheets of the recording material may be adhered together (hereinafter, referred to as a discharged paper adhesion) occurs. Thus, there is a problem in which the qualities of an image formed may be deteriorated.
In order to solve the above problems, methods in which a styrene resin and a polyester resin are grafted with wax have been disclosed (see, for example, JP 07-101318 A, JP 2000-314983 A, and JP 2001-022115 A). In addition, methods, in which a resin obtained by reaction of a polyester resin with part of a styrene resin is used, have been also disclosed (see, for example, JP10-087839 A and JP 2000-275908 A). However, the toner satisfactory overcoming all of those problems has not been provided so far.